Intraocular pressure sensor with external pressure compensation

ABSTRACT

An intraocular pressure sensor system has a first pressure sensor located in an anterior chamber of an eye and a remote pressure sensor located remotely from the first pressure sensor. The remote pressure sensor measures or approximates atmospheric pressure. A difference between readings from the first pressure sensor and the remote pressure sensor approximates intraocular pressure.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/565,907, filed Aug. 3, 2012 which is a division of U.S. applicationSer. No. 12/563,244 filed Sep. 21, 2009, now U.S. Pat. No. 8,257,295.

BACKGROUND OF THE INVENTION

The present invention relates to a device for monitoring intraocularpressure and more particularly to an implantable pressure sensor withexternal pressure compensation.

Glaucoma, a group of eye diseases affecting the retina and optic nerve,is one of the leading causes of blindness worldwide. Glaucoma resultswhen the intraocular pressure (IOP) increases to pressures above normalfor prolonged periods of time. IOP can increase due to an imbalance ofthe production of aqueous humor and the drainage of the aqueous humor.Left untreated, an elevated IOP causes irreversible damage the opticnerve and retinal fibers resulting in a progressive, permanent loss ofvision.

The eye's ciliary body epithelium constantly produces aqueous humor, theclear fluid that fills the anterior chamber of the eye (the spacebetween the cornea and iris). The aqueous humor flows out of theanterior chamber through the uveoscleral pathways, a complex drainagesystem. The delicate balance between the production and drainage ofaqueous humor determines the eye's IOP.

Open angle (also called chronic open angle or primary open angle) is themost common type of glaucoma. With this type, even though the anteriorstructures of the eye appear normal, aqueous fluid builds within theanterior chamber, causing the IOP to become elevated. Left untreated,this may result in permanent damage of the optic nerve and retina. Eyedrops are generally prescribed to lower the eye pressure. In some cases,surgery is performed if the IOP cannot be adequately controlled withmedical therapy.

Only about 10% of the population suffers from acute angle closureglaucoma. Acute angle closure occurs because of an abnormality of thestructures in the front of the eye. In most of these cases, the spacebetween the iris and cornea is more narrow than normal, leaving asmaller channel for the aqueous to pass through. If the flow of aqueousbecomes completely blocked, the IOP rises sharply, causing a suddenangle closure attack.

Secondary glaucoma occurs as a result of another disease or problemwithin the eye such as: inflammation, trauma, previous surgery,diabetes, tumor, and certain medications. For this type, both theglaucoma and the underlying problem must be treated.

FIG. 1 is a diagram of the front portion of an eye that helps to explainthe processes of glaucoma. In FIG. 1, representations of the lens 110,cornea 120, iris 130, ciliary bodies 140, trabecular meshwork 150, andSchlemm's canal 160 are pictured. Anatomically, the anterior chamber ofthe eye includes the structures that cause glaucoma. Aqueous fluid isproduced by the ciliary bodies 140 that lie beneath the iris 130 andadjacent to the lens 110 in the anterior chamber. This aqueous humorwashes over the lens 110 and iris 130 and flows to the drainage systemlocated in the angle of the anterior chamber. The angle of the anteriorchamber, which extends circumferentially around the eye, containsstructures that allow the aqueous humor to drain. The first structure,and the one most commonly implicated in glaucoma, is the trabecularmeshwork 150. The trabecular meshwork 150 extends circumferentiallyaround the anterior chamber in the angle. The trabecular meshwork 150seems to act as a filter, limiting the outflow of aqueous humor andproviding a back pressure producing the IOP. Schlemm's canal 160 islocated beyond the trabecular meshwork 150. Schlemm's canal 160 hascollector channels that allow aqueous humor to flow out of the anteriorchamber. The two arrows in the anterior chamber of FIG. 1 show the flowof aqueous humor from the ciliary bodies 140, over the lens 110, overthe iris 130, through the trabecular meshwork 150, and into Schlemm'scanal 160 and its collector channels.

In glaucoma patients, IOP can vary widely during a 24 hour period.Generally, IOP is highest in the early morning hours before medicationis administered upon waking. Higher pressures damage the optic nerve andcan lead to blindness. Accordingly, it would be desirable to measure IOPover time in order to assess the efficacy of various treatments. Inaddition, continuous IOP data can be used as part of a feedbackmechanism to support an implanted active IOP-controlling system (e.g.valve or pump for controlling aqueous humor flow or delivering drugs).The present invention provides an IOP measuring device.

SUMMARY OF THE INVENTION

In one embodiment consistent with the principles of the presentinvention, the present invention is an intraocular pressure sensorsystem that has a first pressure sensor located in or in fluidiccommunication with the anterior chamber of an eye and a remote pressuresensor located remotely from the first pressure sensor. The remotepressure sensor measures or approximates atmospheric pressure. Adifference between readings from the first pressure sensor and theremote pressure sensor approximates intraocular pressure.

In another embodiment consistent with the principles of the presentinvention, the present invention is an intraocular pressure sensorsystem has a first pressure sensor located in an anterior chamber of aneye and a second pressure sensor located in a drainage location. Adifference between readings from the first pressure sensor and thesecond pressure sensor approximates a pressure differential between theanterior chamber and the drainage location.

In another embodiment consistent with the principles of the presentinvention, the present invention is an intraocular pressure sensorsystem has a first pressure sensor located in a drainage location and aremote pressure sensor located remotely from the first pressure sensor.The remote pressure sensor measures or approximates atmosphericpressure. A difference between readings from the first pressure sensorand the remote pressure sensor approximates pressure in the drainagelocation.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide further explanation of the invention asclaimed. The following description, as well as the practice of theinvention, set forth and suggest additional advantages and purposes ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a diagram of the front portion of an eye.

FIG. 2 is a block diagram of an IOP measuring system according to theprinciples of the present invention.

FIG. 3 is a diagram of an IOP sensor according to the principles of thepresent invention.

FIG. 4 is a diagram of one possible application of the IOP sensor of thepresent invention.

FIG. 5 is an end cap implementation of an IOP sensor consistent with theprinciples of the present invention.

FIGS. 6A and 6B are perspective views of an end cap implementation of anIOP sensor consistent with the principles of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is now made in detail to the exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers are usedthroughout the drawings to refer to the same or like parts.

FIG. 2 is a block diagram of an IOP measuring system 200 according tothe principles of the present invention. In FIG. 2, the IOP measuringsystem includes power source 205, IOP sensor 210 (which can include P1,P2, and/or P3), processor 215, memory 220, data transmission module 225,and optional speaker 230.

Power source 205 is typically a rechargeable battery, such as a lithiumion or lithium polymer battery, although other types of batteries may beemployed. In addition, any other type of power cell is appropriate forpower source 205. Power source 205 provides power to the system 200, andmore particularly to processor 215. Power source can be recharged via anRFID link or other type of magnetic coupling.

Processor 215 is typically an integrated circuit with power, input, andoutput pins capable of performing logic functions. In variousembodiments, processor 215 is a targeted device controller. In such acase, processor 215 performs specific control functions targeted to aspecific device or component, such as a data transmission module 225,speaker 230, power source 205, or memory 220. In other embodiments,processor 215 is a microprocessor. In such a case, processor 215 isprogrammable so that it can function to control more than one componentof the device. In other cases, processor 215 is not a programmablemicroprocessor, but instead is a special purpose controller configuredto control different components that perform different functions.

Memory 220 is typically a semiconductor memory such as NAND flashmemory. As the size of semiconductor memory is very small, and thememory needs of the system 200 are small, memory 220 occupies a verysmall footprint of system 200. Memory 220 interfaces with processor 215.As such, processor 215 can write to and read from memory 220. Forexample, processor 215 can be configured to read data from the IOPsensor 210 and write that data to memory 220. In this manner, a seriesof IOP readings can be stored in memory 220. Processor 215 is alsocapable of performing other basic memory functions, such as erasing oroverwriting memory 220, detecting when memory 220 is full, and othercommon functions associated with managing semiconductor memory.

Data transmission module 225 may employ any of a number of differenttypes of data transmission. For example, data transmission module 225may be active device such as a radio. Data transmission module 225 mayalso be a passive device such as the antenna on an RFID tag. In thiscase, an RFID tag includes memory 220 and data transmission module 225in the form of an antenna. An RFID reader can then be placed near thesystem 200 to write data to or read data from memory 220. Since theamount of data typically stored in memory 220 is likely to be small(consisting of IOP readings over a period of time), the speed with whichdata is transferred is not crucial. Other types of data that can bestored in memory 220 and transmitted by data transmission module 225include, but are not limited to, power source data (e.g. low battery,battery defect), speaker data (warning tones, voices), IOP sensor data(IOP readings, problem conditions), and the like.

Optional speaker 230 provides a warning tone or voice to the patientwhen a dangerous condition exists. For example, if IOP is at a levelthat is likely to lead to damage or presents a risk to the patient,speaker 230 may sound a warning tone to alert the patient to seekmedical attention or to administer eye drops. Processor 215 reads IOPmeasurements from IOP sensor 210. If processor 215 reads one or a seriesof IOP measurements that are above a threshold, then processor 215 canoperate speaker 230 to sound a warning. The threshold can be set andstored in memory 220. In this manner, an IOP threshold can be set by adoctor, and when exceeded, a warning can be sounded.

Alternatively, data transmission module may be activated to communicatean elevated IOP condition to a secondary device such as a PDA, cellphone, computer, wrist watch, custom device exclusively for thispurpose, remote accessible data storage site (e.g. an internet server,email server, text message server), or other electronic device. In oneembodiment, a personal electronic device uploads the data to the remoteaccessible data storage site (e.g. an internet server, email server,text message server). Information may be uploaded to a remote accessibledata storage site so that it can be viewed in real time, for example, bymedical personnel. In this case, the secondary device may contain thespeaker 230. For example, in a hospital setting, after a patient hasundergone glaucoma surgery and had system 200 implanted, a secondarydevice may be located next to the patient's hospital bed. Since IOPfluctuations are common after glaucoma surgery (both on the high sideand on the low side which is also a dangerous condition), processor 215can read IOP measurements made by an implanted IOP sensor 210. Ifprocessor 215 reads an unsafe IOP condition, data transmission module225 can alert the patient and medical staff via speaker 230 or bytransmitting the unsafe readings to a secondary device.

Such a system is also suitable for use outside a hospital setting. Forexample, if an unsafe IOP condition exists, processor 215 can operatespeaker 230 to sound an audible warning. The patient is then alerted andcan seek medical attention. The warning can be turned off by a medicalprofessional in a number of ways. For example, when data transmissionmodule 225 is an RFID tag, an RFID link can be established between anexternal device and system 200. This external device can communicatewith system 200 to turn off the speaker 230. Alternatively, an opticalsignal may be read by system 200. In this case, data transmission module225 has an optical receptor that can receive a series of light pulsesthat represent a command—such as a command to turn off speaker 230.

FIG. 3 is a diagram of an IOP sensor according to the principles of thepresent invention. In FIG. 3, the IOP sensor consists of three pressuresensors, P1, P2, and P3, a drainage tube 430, valve 420, and divider350. Pressure sensor P1 is located in or is in fluidic communicationwith the anterior chamber 340, pressure sensor P2 is located at adrainage site in the subconjunctival space, and pressure sensor P3 islocated remotely from P1 and P2. Pressure sensor P1 can also be locatedin a lumen or tube that is in fluid communication with the anteriorchamber. As such, pressure sensor P1 measures a pressure in the anteriorchamber, pressure sensor P2 measures a pressure at a drainage site, andpressure sensor P3 generally measures or corresponds to atmosphericpressure.

In FIG. 3, tube 430 drains aqueous from the anterior chamber 340 of theeye. A valve 420 controls the flow of aqueous through the tube 430.Pressure sensor P1 measures the pressure in the tube 430 upstream fromthe valve 420 and downstream from the anterior chamber 340. In thismanner, pressure sensor P1 measures the pressure in the anterior chamber340. The expected measurement discrepancy between the true anteriorchamber pressure and that measured by P1 when located in a tubedownstream of the anterior chamber (even when located between the scleraand the conjunctiva) is very minimal. For example, Poiseuille's law forpipe flow predicts a pressure drop of 0.01 mmHg across a 5-millimeterlong tube with a 0.300 millimeter inner diameter for a flow rate of 3microliters per minute of water.

A divider 350 separates pressure sensor P2 from pressure sensor P3.Pressure sensor P2 is located at a drainage site (e.g. 410 in FIG. 4).As such, pressure sensor P2 is located in a pocket that generallycontains aqueous—it is in a wet location. Pressure sensor P3 isphysically separated from pressure sensor P2 by divider 350. Divider 350is a physical structure that separates the wet location of P2 from thedry location of P3. Divider 350 is included when the system of thepresent invention is located on a single substrate. In thisconfiguration, all three pressure sensors (P1, P2, and P3) are locatedon a substrate that includes tube 430, valve 420, divider 350, and theother components of the system.

In one embodiment of the present invention, pressure sensor P3 islocated in close proximity to the eye. Pressure sensor P3 may beimplanted in the eye under the conjunctiva. In such a case, pressuresensor P3 measures a pressure that can be correlated with atmosphericpressure. For example, true atmospheric pressure can be a function ofthe pressure reading of pressure sensor P3. P3 may also be located in adry portion of the subconjunctival space, separate from the drainagelocation. Regardless of location, pressure sensor P3 is intended tomeasure atmospheric pressure in the vicinity of the eye or at the eye'ssurface.

Generally, IOP is a gauge pressure reading—the difference between theabsolute pressure in the eye (as measured by P1) and atmosphericpressure (as measured by P3). Atmospheric pressure, typically about 760mm Hg, often varies in magnitude by 10 mmHg or more. For example,atmospheric pressure can vary significantly if a patient goes swimming,hiking, etc. Such a variation in atmospheric pressure is significantsince IOP is typically in the range of about 15 mm Hg. Thus, for 24 hourmonitoring of IOP, it is desirable to have pressure readings for theanterior chamber (as measured by P1) and atmospheric pressure in thevicinity of the eye (as measured by P3).

Therefore, in one embodiment of the present invention, pressure readingsare taken by P1 and P3 simultaneously or nearly simultaneously over timeso that the actual IOP can be calculated (as P1−P3 or P1−f(P3)). Thepressure readings of P1 and P3 can be stored in memory 220 by processor215. They can later be read from memory so that actual IOP over time canbe interpreted by a physician.

Pressure sensors P1, P2, and P3 can be any type of pressure sensorsuitable for implantation in the eye. They each may be the same type ofpressure sensor, or they may be different types of pressure sensors. Forexample, pressure sensors P1 and P2 may be the same type of pressuresensor (implanted in the eye), and pressure sensor P3 may be a differenttype of pressure sensor (in the vicinity of the eye).

In another embodiment of the present invention, pressure readings takenby pressure sensors P1 and P2 can be used to control a device thatdrains aqueous from the anterior chamber 340. FIG. 4 is a diagram of onepossible application of the IOP sensor of the present invention thatutilizes the readings of pressures sensors P1 and P2. In FIG. 4,pressure sensor P1 measures the pressure in the anterior chamber 340 ofthe eye. Pressure sensor P2 measures the pressure at a drainage site410.

Numerous devices have been developed to drain aqueous from the anteriorchamber 340 to control glaucoma. Most of these devices are variations ofa tube that shunts aqueous from the anterior chamber 340 to a drainagelocation 410. For example, tubes have been developed that shunt aqueousfrom the anterior chamber 340 to the subconjunctival space thus forminga bleb under the conjunctiva or to the subscleral space thus forming ableb under the sclera. (Note that a bleb is a pocket of fluid that formsunder the conjunctiva or sclera). Other tube designs shunt aqueous fromthe anterior chamber to the suprachoroidal space, the supraciliaryspace, the juxta-uveal space, or to the choroid. In other applications,tubes shunt aqueous from the anterior chamber to Schlemm's canal, acollector channel in Schlemm's canal, or any of a number of differentblood vessels like an episcleral vein. Some tubes even shunt aqueousfrom the anterior chamber to outside the conjunctiva. Finally, in someapplications, no tube is used at all. For example, in a trabeculectomy(or other type of filtering procedure), a small hole is made from thesubconjunctival or subscleral space to the anterior chamber. In thismanner, aqueous drains from the anterior chamber, through the hole, andto a bleb under the conjunctiva or sclera. Each of these differentanatomical locations to which aqueous is shunted is an example of adrainage location 410.

In FIG. 4, a tube 430 with a valve 420 on one end is located with oneend in the anterior chamber 340 and the other end in a drainage location410. In this manner, the tube 430 drains aqueous from the anteriorchamber 340 to the drainage location 410. Valve 420 controls the flow ofaqueous from anterior chamber 340 to drainage location 410. Pressuresensor P1 is located in the anterior chamber or in fluid communicationwith the anterior chamber 340. As shown in the embodiment of FIG. 3,pressure sensor P1 is located upstream from valve 420. In this manner,pressure sensor P1 is located in the subconjunctival space but is influid communication with the anterior chamber 340.

Since pressure sensor P1 measures the pressure in the anterior chamber340 and pressure sensor P2 measures pressure at the drainage location410, the difference between the readings taken by these two pressuresensors (P1−P2) provides an indication of the pressure differentialbetween the anterior chamber 340 and the drainage location 410. In oneembodiment, this pressure differential dictates the rate of aqueous flowfrom the anterior chamber 340 to the drainage location 410.

One complication involved with filtering surgery that shunts theanterior chamber 340 to a drainage location 410 is hypotony—a dangerousdrop in IOP that can result in severe consequences. It is desirable tocontrol the rate of aqueous outflow from the anterior chamber 340 to thedrainage location 410 so as to prevent hypotony. Readings from pressuresensor P1 and pressure sensor P2 can be used to control the flow ratethrough tube 430 by controlling valve 420. For example, valve 420 can becontrolled based on the pressure readings from pressure sensor P1 andpressure sensor P2.

In another embodiment of the present invention, IOP (based on readingsfrom pressure sensor P1 and pressure sensor P3) can be controlled bycontrolling valve 420. In this manner, IOP is the control parameter.Valve 420 can be adjusted to maintain a particular IOP (like an IOP of15 mm Hg). Valve 420 may be opened more at night than during the day tomaintain a particular IOP. In other embodiments, an IOP drop can becontrolled. Immediately after filtering surgery, IOP can dropprecipitously. Valve 420 can be adjusted to permit a gradual drop in IOPbased on readings from pressure sensors P1 and P3.

In another embodiment of the present invention, readings from pressuresensor P2 (or from the difference between pressure sensor P2 andatmospheric pressure as measured by P3) can be used to control valve 420so as to control the morphology of a bleb. One of the problemsassociated with filtering surgery is bleb failure. A bleb can fail dueto poor formation or fibrosis. The pressure in the bleb is one factorthat determines bleb morphology. Too much pressure can cause a bleb tomigrate to an undesirable location or can lead to fibrosis. The pressureof the bleb can be controlled by using the reading from pressure sensorP2 (at drainage location 410—in this case, a bleb). In one embodiment ofthe present invention, the difference between the pressure in the bleb(as measured by P2) and atmospheric pressure (as measured by P3) can beused to control valve 420 to maintain a desired bleb pressure. In thismanner, the IOP pressure sensor of the present invention can also beused to properly maintain a bleb.

Valve 420 can be controlled by microprocessor 215 or a suitable PIDcontroller. A desired pressure differential (that corresponds to adesired flow rate) can be maintained by controlling the operation ofvalve 420. Likewise, a desired IOP, IOP change rate, or bleb pressurecan be controlled by controlling the operation of valve 420.

While valve 420 is depicted as a valve, it can be any of a number ofdifferent flow control structures that meter, restrict, or permit theflow of aqueous from the anterior chamber 340 to the drainage location410. In addition, valve 420 can be located anywhere in or along tube430.

Finally, there are many other similar uses for the present IOP sensor.For example, various pressure readings can be used to determine if tube420 is occluded or obstructed in some undesirable manner. As such,failure of a drainage device can be detected. In a self clearing lumenthat shunts the anterior chamber 340 to a drainage location 410, anundesirable blockage can be cleared based on the pressure readings ofP1, P2, and/or P3.

FIG. 5 is an end cap implementation of an IOP sensor consistent with theprinciples of the present invention. In FIG. 5, pressure sensors P1 andP3 are integrated into an end cap 510. End cap 510 fits in tube 430 soas to form a fluid tight seal. One end of tube 430 resides in theanterior chamber 340, and the other end of tube 430 (where end cap 510is located) is located outside of the anterior chamber 340. Typically,one end of tube 430 resides in the anterior chamber 340, and the otherend resides in the subconjunctival space. In this manner, pressuresensor P1 is in fluid communication with the anterior chamber 340. Sincethere is almost no pressure difference between the anterior chamber 340and the interior of tube 430 that is in fluid contact with the anteriorchamber 340, pressure sensor P1 measures the pressure in the anteriorchamber 340. Pressure sensor P3 is external to the anterior chamber 340and either measures atmospheric pressure or can be correlated toatmospheric pressure.

Typically, tube 430 is placed in the eye to bridge the anterior chamber340 to the subconjunctival space, as in glaucoma filtration surgery. Inthis case, P3 resides in the subconjunctival space. In thisconfiguration, P3 measures a pressure that is either very close toatmospheric pressure or that can be correlated to atmospheric pressurethrough the use of a simple function. Since plug 510 provides a fluidtight seal for tube 430, pressure sensor P3 is isolated from pressuresensor P1. Therefore, an accurate IOP reading can be taken as thedifference between the pressure readings of P1 and P3 (P1−P3). In oneembodiment, a single, thin membrane 520 resides in the sensor packageand is exposed to P1 on one side (tube side) and P3 on the other side(isolation side), and thus the net pressure on the membrane 520 isrecorded by the sensor, providing a gauge reading corresponding IOP.

FIGS. 6A and 6B are perspective views of the end cap implementation ofFIG. 5. In this embodiment, pressure sensor P1 is located on one end ofend cap 510 so that it can be located inside tube 430. Pressure sensorP3 is located on the other end of end cap 510 so that it can be locatedoutside of tube 430. A membrane (520) separates P1 from P3. In thismanner, pressure sensor P1 is isolated from pressure sensor P3. Whilepressure sensors P1 and P3 are depicted as being located on oppositesurfaces of a membrane 520 in the end cap 510, they can also be locatedintegral with end cap 510 in any suitable position to facilitate thepressure measurements.

From the above, it may be appreciated that the present inventionprovides a system for measuring IOP. The present invention provides anIOP sensor with external pressure compensation. The present invention isillustrated herein by example, and various modifications may be made bya person of ordinary skill in the art.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A glaucoma treatment device comprising: an endcap with proximal and distal ends; an anterior chamber pressure sensorintegrated with and located at the proximal end of the end cap and influid communication with an anterior chamber of an eye; a remotepressure sensor, the remote pressure sensor measures or approximatesatmospheric pressure, the remote pressure sensor integrated with andlocated at the distal end of the end cap and under a conjunctiva of theeye; and a tube with proximal and distal ends, the tube fluidly couplingthe anterior chamber to a location outside the anterior chamber whereinthe end cap is located in and seals the distal end of the tube; whereinthe end cap is configured to be located in the eye.
 2. The glaucomatreatment device of claim 1 wherein the remote pressure sensor islocated in a subconjunctival space of the eye.
 3. The glaucoma treatmentdevice of claim 1 further comprising: a membrane separating the anteriorchamber pressure sensor from the remote pressure sensor.
 4. The glaucomatreatment device of claim 1 wherein the remote pressure sensorapproximates atmospheric pressure based on a correlation between ameasured pressure and atmospheric pressure.
 5. The glaucoma treatmentdevice of claim 1 wherein the end cap is located in a subconjunctivalspace of the eye.
 6. A glaucoma treatment device comprising: an end capwith proximal and distal ends, the end cap of a suitable size and shapeto be located under a conjunctiva of an eye; an anterior chamberpressure sensor integrated with and located at the proximal end of theend cap and in fluid communication with an anterior chamber of an eye; aremote pressure sensor, the remote pressure sensor measures orapproximates atmospheric pressure, the remote pressure sensor integratedwith and located at the distal end of the end cap and under theconjunctiva of the eye; and a tube with proximal and distal ends, thetube of suitable size to be implanted in the eye, the tube fluidlycoupling the anterior chamber to a location under the conjunctiva of theeye, wherein the end cap is located in and seals the distal end of thetube such that the proximal end of the end cap is located in the tubeand the distal end of the end cap is located outside the tube.
 7. Theglaucoma treatment device of claim 6 further comprising: a membraneseparating the anterior chamber pressure sensor and the remote pressuresensor.
 8. The glaucoma treatment device of claim 6 wherein the remotepressure sensor approximates atmospheric pressure based on a correlationbetween a measured pressure and atmospheric pressure.